1. Field of the Invention
The present invention relates generally to a shearing machine for cutting or shearing sheet-like workpieces such as sheet metals. More particularly, the present invention pertains to a shearing machine which is provided with two pairs of upper and lower blades in a manner such that the upper and lower of one pair are connected to the upper and lower blades, respectively, of the other pair at right angles to shear right-angled blanks out of sheet-like workpieces.
2. Description of the Prior Art
As is well-known, generally shearing machines for cutting or shearing sheet-like workpieces such as sheet metals are each provided with an elongated movable upper blade carried by a ram member and an elongated fixed lower blade which is fixedly provided under the upper blade to cooperate therewith. The ram member carrying the upper blade is so arranged as to be mechanically or hydraulically moved up and down to bring the upper blade into and out of engagement with the lower blade to cut or shear the workpieces. Also, the ram member is straightly or vertically moved up and down in what is called a guillotine-type shearing machine, and it is swung up and down around a pivot means in what is called a swing-type shearing machine. Generally, the swing-type shearing machines can be manufactured and assembled at lower costs than the guillotine-type shearing machines. Also, the upper blade is so disposed as to be inclined or tilted at an angle that is shear angle to the lower blade so as to decrease the shearing force required. However, too large shear angle of the upper blade to the lower blade will cause the workpieces being sheared to be deformed or twisted.
Heretofore, there have been shearing machines which are each provided with two pair of upper and lower blades in a manner such that the upper and lower blades of one pair are connected to the upper and lower blades, respectively, of the other pair at right angles so as to shear right-angled blanks out of sheet-like workpieces. Such shearing machines have been variously disclosed in U.S. Pat. Nos. 3,215,017; 2,964,984; 2,654,428; 3,205,748; 3,616,719; 1,416,800; 1,447,247 and 3,691,887 for example. In such a shearing machine, the upper blades are mounted at the right angle to each other on a ram member which is movable up and down in a frame having a C-shaped throat into which a workpiece to be sheared is to be fed, while the lower blades are fixedly mounted at the right angle to each other on a portion of the frame. Of course, the arrangement is such that the upper blades are moved up and down by the ram member into and out of engagement with the lower blades to cooperate therewith to shear right-angled blanks out of a workpiece which is fed into the throat.
Heretofore, it has been disadvantageous that the shearing machines each having the two pairs of upper and lower blades as described above are costly in that they are constructed in the guillotine-type manner so that the ram member is straightly or vertically moved up and down. There may have been some shearing machines of the swing-type in which the ram member carrying the two upper blades is swung up and down on a pivot means as has been disclosed in the U.S. Pat. No. 3,691,887 listed above. Indeed, it will be easily thinkable that the ram member carrying the two upper blades can be so arranged as to be swung up and down on a pivot means with one of the two upper blades disposed in parallel with the pivot means and with the other upper blade perpendicular to the pivot means. In this manner, however, it is practically disadvantageous that the shear angle of the upper blade perpendicular to the pivot means will be largely changed and become too large with regard to the mate lower blade since the upper blade perpendicular to the pivot means is rotated around the pivot means as the ram member is swung therearound. Of course, if the shear angle of the upper blade to the lower blade is largely changed and becomes too large during a shearing operation, the upper and lower blades cannot make an accurate shearing action with the result that the workpiece to be sheared will be deformed and twisted. Thus, it must be that there has been no swing-type shearing machine that is capable of making an accurate shearing action to shear right-angled blanks out of sheet-like workpieces, in spite of the fact that the swing-type shearing machines can be manufactured and assembled at lower costs.
Another disadvantage with regard to the conventional shearing machines having two pairs of upper and lower blades has been the fact that a workpiece larger in width than the horizontal depth or length of the throat of the machine frame cannot be sheared. In other words, it has been disadvantageous in the conventional shearing machines that the maximum width of workpieces capable of being sheared is limited to the horizontal depth of the throat formed in the machine frame.